1. Field of the Invention
The present invention relates to a throttle valve control device used for an internal-combustion engine and, more specifically, to a throttle valve structure which provides a clearance with respect to a throttle bore so as to allow a throttle valve to further rotate from a full closed position in a reverse rotating direction at throttle valve non-control time, while providing the minimum open area at idle engine time, and a producing method of such the throttle valve.
2. Description of Related Art
Conventionally, there has been proposed a butterfly-valve type throttle valve mounted in an intake passage by means of a throttle shaft extending across the passage and used for controlling the amount of air to be supplied to an engine. One example of such a throttle valve is shown in FIG. 6A. A throttle valve 13 illustrated by a solid line in FIG. 6A is held as inclined at a predetermined set angle xcex3 from a horizontal position in a throttle bore 11a forming an intake passage. This state is a full closed position, namely, an opening angle for the minimum flow rate of air. It is to be noted that the throttle valve 13 is rotated in a normal rotating direction (in a counterclockwise direction in the figure) from the full closed position to slightly open at idle operation of an engine. At this time, the valve 13 is operated with an open area shown by the diagonally shaded area in FIG. 6B. Therefore, viewing this throttle valve 13 from right above, perpendicular to its upper face, or showing it in plan view, as shown in FIG. 7B, the valve 13 has an elliptic shape with a major axis in a direction perpendicular to a center line 13c connecting screws 14 and 15, namely, a center axis of rotation of the valve 13.
Meanwhile, as disclosed in Japanese patent application laid-open No. 10-163827 (which corresponds to U.S. patent application Ser. No. 09/318,252) filed by the same applicant as that of the present invention, there has been proposed a throttle valve control device in which a throttle valve is further rotated by a predetermined angle from a full closed position in a reverse rotating direction to stop an engine at throttle valve non-control time such as engine stop.
If the throttle valve 13 having the above configuration is adopted in the throttle valve control apparatus disclosed in Japanese patent application laid-open No. 10-163827, the following disadvantages may rise.
FIG. 7A is a sectional view showing an operating state of the throttle valve 13 in the throttle valve control apparatus wherein the valve will be further rotated from a full closed position indicated by a solid line in the figure in a reverse direction (clockwise in the figure) at throttle valve non-control time. In the above throttle valve control apparatus, as shown in FIG. 7B, if a clearance B needed for reverse rotation of the valve 13 is provided between the edge 13d in the major axis of the valve 13 positioned in the full closed position (a horizontal position) and the inner wall of a throttle bore 11a, a clearance C larger than the clearance B is produced in the vicinity of the rotating axis. Accordingly, the open area between the valve 13 and the bore 11a becomes so excessively large that the minimum open area needed for idle engine operation could not be ensured.
On the other hand, an example of adopting a throttle valve 16 of a perfect circular shape in order to facilitate the reverse rotation is shown in FIG. 7C. When a clearance D needed for the reverse rotation of the valve 16 is produced between an edge 16d of the valve 16 and the bore 11a, the same clearance as D is produced in the vicinity of the rotating axis. As is the above case, the minimum open area needed for idle engine operation could not be ensured.
It is to be noted that the clearances shown by the shaded areas in FIGS. 6B, 7B and 7C are exaggerated in shape and size than actual shape and size for the purpose of facilitating explanations.
The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a throttle valve control device capable of easily further rotating a throttle valve by a predetermined angle from a full closed position in a reverse rotating direction at throttle valve non-control time, while providing the minimum open area needed for maintaining a smooth idle engine operation, and a producing method of the throttle valve.
Additional objects and advantages of the invention will be set forth in part in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the purpose of the invention, there is provided a throttle valve control device provided with a throttle valve for opening and closing an intake passage of an engine and a throttle shaft extending across the intake passage, the throttle valve being fixed to the throttle shaft and rotated in a normal direction from a full closed position to a full open position and in a reverse direction from the full open position to the full closed position to control output of the engine, and further rotated by a predetermined angle in the reverse direction from the full closed position to a predetermined open position at stop of the engine, wherein the throttle valve is formed in an elliptic shape of which a major axis is a center line connecting a plurality of mounting holes for fixing the throttle valve to the throttle shaft.
According to another aspect of the present invention, there is provided a throttle valve for opening and closing an intake passage of an engine, the throttle valve having an elliptic outer shape of which a major axis is a center line connecting a plurality of mounting holes for fixing the throttle valve to a throttle shaft.
Furthermore, according to another aspect of the present invention, there is provided a producing method of a throttle valve used in the throttle valve control device according to claim 1, the method including the steps of: holding a throttle valve material in a machine tool such that the center line connecting the mounting holes is inclined at a predetermined inclination angle with respect to a plane perpendicular to a processing axis of the machine tool; processing an outer periphery of the throttle valve material; reversing the throttle valve material 180xc2x0 about the center line; and processing again the outer periphery to provide an elliptic throttle valve having predetermined major and minor axis diameters.